1. Field of the Invention
This application is filed under 35 U.S.C. 371 and claims priority based upon international application PCT/EP96/03039, filed on Jul. 11, 1996, which claims priority based upon German Patent Application P19525699.9, filed on Jul. 14, 1995.
The invention relates to a tandem turbine-blade cascade of a turbo-engine, power engine or other machine, having at least two rows of blades disposed substantially directly in line with one another in the rotor or stator. A turbocompressor with this kind of tandem turbine-blade cascade is shown for instance in German Patent DE 36 24 951 C1.
2. Description of the Related Art
Such tandem turbine-blade cascades can be provided in particular in turbine aircraft engines, in the compressor or the turbine, in order to achieve the pressure ratios needed in as few stages as possible. This leads to a desired weight reduction, but on the other hand, puts a greater aerodynamic load on the individual stage. Especially for the case of a compressor stage, this means that among other things that a greater deflection and/or retardation in the flow must be effected in the rotor with regard to the relative system, or in the ensuing stator with regard to the absolute system. However, this is possible only to a limited extent, since an excessive aerodynamic load on the cascade leads to a flow separation and thus, to increased pressure losses. These losses can be reduced if the cascade load is divided between two rows of blades disposed substantially directly one behind the other or directly in a line in the rotor or stator. The two rows of blades disposed substantially in a line may be positioned differently relative to one another in both the axial and circumferential directions, which affects the pressure index and the efficiency. In this regard, reference may be made to the studies by Linnemann reported in the German Journal "Konstruktion" [Construction] 1964, No. 4, p. 128. With regard to the phrase "substantially directly", reference is briefly made to FIG. 1, later to be described in further detail, which is taken from precisely this reference in the literature (Linnemann). Here, one can see the two rows 1, 2 of blades, for instance in a rotor, which are spaced apart from one another by the dimension a*, and between which no further row of blades, for instance of a stator, protrudes. Each value a*, which is less than the chord length c and can even assume negative values, is intended to represent substantially in-line rows 1, 2 of blades as long as no further row of blades protrudes between these rows of blades.
If the second or subsequent row of blades is now heavily loaded aerodynamically in such a way that a larger number of blades would have to be provided in this row of blades than in the preceding row of blades, then for some of the blades in the second row, the result can be unfavorable positions in the circumferential direction, in terms of the pressure index and efficiency. The object of the present invention is to disclose remedies for these problems.